Enhanced docosahexaenoic acid production of Schizochytrium sp. H016 utilizing rapeseed meal hydrolysate

Rapeseed meal hydrolysate (RSMH), is a low-cost, nitrogen-rich substrate with high potential for microbial fermentation. This study investigated the feasibility of using RSMH as an alternative nitrogen source to enhance docosahexaenoic acid (DHA) production in Schizochytrium sp. H016. Nutritional analysis revealed that RSMH contains abundant amino acids and phenolics, which are favorable for microbial growth and stress tolerance. Fermentation results showed that replacing yeast extract with RSMH significantly improved biomass accumulation, lipid production, and DHA yield. At 120 h, the maximum biomass, lipid, and DHA yields reached 45.80 g/L, 18.62 g/L, and 7.30 g/L, respectively, corresponding to increases of 23.96 %, 97.66 %, and 94.15 % compared to the control. RT-qPCR analysis revealed that RSMH upregulated key genes involved in glycolysis, fatty acid biosynthesis, triacylglycerol assembly, and antioxidant defense, which together promoted carbon flux toward lipid synthesis and improved oxidative stress resistance. Confocal microscopy further confirmed the increased accumulation of lipid droplets in RSMH medium. Fed-batch fermentation in a 5-L bioreactor yielded DHA and lipids of 15.51 and 33.81 g/L, respectively, with a final biomass of 63.80 g/L. These findings demonstrate that RSMH effectively substitutes yeast extract and upgrades rapeseed meal into a feedstock for DHA production.